8 IOWA STUDIES IN NATURAL HISTORY 



lessness of physiographic interpretation during this time 

 was followed by a period of reaction ushered in by the 

 criticism of Tarr^ who seems to have been the first to sound 

 a note of warning and present the idea that not all flattish 

 surfaces above streams are old peneplains. 



But now Tarr's argument in turn seems to have been 

 carried beyond the point intended by its author, for many 

 geologists having convinced themselves and others that 

 some physiographic features which have been described as 

 raised peneplains are not old erosion surfaces, have pro- 

 ceeded to the extreme conclusion that there are no such 

 things as raised peneplains and consider no evidence either 

 in favor of or against the peneplain theory in working out 

 the histories of regions in the field. The conclusion that 

 because some upland flats are not old peneplains there is 

 no such thing as raised peneplains is as unwarranted and 

 as great a detriment in the search for truth as was the con- 

 clusion of the older physiographers that because some up- 

 land surfaces were old peneplains, all such surfaces could 

 be identically interpreted. 



The extreme reaction against the peneplain theory seems 

 to be giving way at present to a revival of interest in the 

 subject, as shown in the spirited discussion among Umple- 

 by-, Atwood", Blackwelder^ and Rich'', all of whom assume 

 the existence of a raised peneplain and differ among them- 

 selves only in regard to the age of the plain. R. T. Cham- 

 berlin" also clearly believes in the peneplain theory, as evi- 

 denced in one of his latest productions. Physiographers seem 

 still to be about evenly divided into two groups, the mem- 

 bers of one of which disregard the peneplain theory en- 



1. Tarr. Ralph S., "The Peneplain," Am. Geol. Vol. XXI (1898), pp. 351-371. 



2. Umpleby, Joseph B., "An Old Erosion Surface in Idaho — Its Age and Value as a 

 Datum Plane," Jour. GeoL, Vol. XX, No. 2, pp. 139-147 ; "An Old Erosion Surface in 

 Eastern Utah — Its Aire and Value in Time Determination," Abstract, Waah. Acad. 

 Sci. Jour., Vol. 2, pp. 109-110, 1912; "The Old Erosion Surface in Idaho," Jour. 

 GeoL. Vol. XXI. pp. 224 et seq, 1918. 



3. Atwood, Wallace W., "The Physiosriaphic Conditions at Butte, Montana and 

 Binsrham Canyon, Utah When the Copper Ores in These Districts were Enriched," 

 Econ. GeoL, Vol. XI, pp. 687-740, 1916 : "Physiosraphie Conditions and Copper En- 

 richment," Econ. GcoL, Vol. XII, pp. 545-547, 1917. 



4. Blackwelder, E.. "Physiosraphic Conditions and Copper Enrichment," Econ. 

 GcoL, Vol. XII, pp. 541-545. 1917. 



5. Rich, .John L., "An Old Ei'osion Surface in Idaho: Is it Eocene," Econ. GcoL, 

 Vol. XIII, No. 2, March, 1918. 



6. Chamberlin, R. T., "The Building of the Colorado Rockies," Jour. GcoL, Vol. 

 XXVII, pp. 145-251. 



